1. Field of the Inventions
Methods and devices are disclosed herein for therapeutically treating tissue. In one example, the devices and methods are suitable for minimally invasive surgery. More particularly, methods and devices described herein permit creating an ablation pattern on an organ while reducing excessive trauma to a patient. The methods and devices also allow for improved access within a body cavity to perform a surgical procedure, for example ablation and/or coagulation of cardiac tissue during minimally invasive surgical access to the heart.
2. Description of the Related Art
Atrial fibrillation surgery requires creation of an ablation or coagulation lesion in atrial tissue. Typically, a physician creates a lesion using energy (including but not limited to radiofrequency, D.C., microwave, laser or other thermal modalities) to prevent wavelets or electrical signals/impulses that propagate through the atrial tissue to sustain atrial fibrillation or produce atrial flutter, atrial tachycardia, or other arrhythmia.
Many conventional approaches in applying energy to the atrial tissue face difficulties in attempting to create a complete lesion pattern that prevents propagation of the electrical impulse across the lesion pattern. Some factors attributable to these difficulties are tissue contact throughout the length of the electrode(s) is/are not consistent causing variability in the transmission of energy throughout the target length of ablated/coagulated tissue. Moreover, surrounding anatomic features also contributes to the difficulty in creating a complete lesion pattern. As a result, an incomplete lesion or lesion pattern includes one or more gaps of viable or semi-viable tissue that allows propagation of wavelets through tissue and through the lesion pattern.
Another factor in the inability of existing thermal ablation systems to create complete curvilinear, transmural lesions is the presence of convective cooling on the opposite surface of the atrium. This convective cooling produces a heat sink that decreases the maximum temperature at this surface thereby preventing the lesions from consistently extending transmurally through the entire wall of the atrium. This is especially relevant during beating-heart procedures in which the coagulation/ablation probe is placed against the epicardial surface, and blood flowing along the endocardium removes heat thus producing a larger gradient between temperature immediately under the electrodes along the epicardium and that the temperature at the endocardium.
Yet another other deficiency of current approaches is the inability to direct the coagulation of precise regions of soft tissue while avoiding underlying or nearby tissue structures. For example, atrial fibrillation ablation may involve extending a lesion to the annulus near which the circumflex, right coronary artery, and coronary sinus reside; another example involves ablating ventricular tachycardia substrates that reside near coronary arteries or coronary veins. Conventional approaches are unable to selectively ablate desired soft tissue structures and isolate preserved tissue structures from targeted regions.
Traditionally, atrial coagulation patterns were only completed using endocardial coagulation lesions. In such procedures, the physician introduced one or more intravenous catheters through the vasculature to atrial tissue. Endocardial coagulation suffers a drawback in that the physician cannot easily visualize the site being ablated. Furthermore, endocardial coagulation carry a risk of complications due to ablating outward from the endocardial surface including esophageal fistula, thromboembolic complications from coagulum formation, PV stenosis, phrenic nerve palsy and lung damage. Aside from the risks, it is difficult to create complete linear lesion lines via an endocardial approach.
Recently, systems have been developed to ablate the cardiac tissue on the epicardium. Epicardial coagulation allows for more comprehensive bi-atrial lesion patterns at the expense of procedural complexity and time. However, many current procedures require significant manipulation of other tissue structures to create the desired lesion pattern. For example, many procedures require one or more ports or trocars placed in a chest wall and/or deflation of a lung to access the target site. Furthermore, many existing procedures require dissection of pericardial reflections to create a full lesion pattern. Dissection of these pericardial reflections presents many additional complications. For example, the tissue surrounding the reflections is very delicate and can be easily damaged during creation of the lesion, or when dissecting the reflection. Visualization is difficult during dissecting of a pericardial reflection so any inadvertent dissection out-of-plane could cause dissection of other tissue structures. For instance, inadvertent dissection of a pulmonary vein can obviously cause significant harm to a patient.
A convergent coagulation pattern utilizes both endocardial and epicardial lesions provide a technique that is comprehensive, bi-atrial and simpler than an epicardial or endocardial procedure alone. In one variation of this convergent procedure, a physician is able to accurately determine the perimeter or outline of a lesion on one side of tissue from an opposite side of the tissue. This allow for improved placement of the lesions and produces the convergent coagulation pattern without creating significant gaps that allow electrical impulses to pass therethrough in tissue.
The improved methods and devices described herein offer improved access to tissue regions within the body, especially those organs in the thoracic cavity. Variations of these methods and devices address the above described deficiencies for atrial fibrillation and ventricular tachycardia ablation. In addition, the embodiments or variations of the embodiments may address similar deficiencies, which are apparent during other applications involving coagulation of a selected tissue region in a precise manner.